The present invention relates to a method of reprocessing cured polysulfide and/or polymercaptan elastomers.
This kind of elastomer occurs as a resulting residual material in the processing of reactive one-component or multi-component polysulfide and/or polymercaptan prepolymers to form sealing or coating compositions.
Residual amounts of liquid and pasty individual components of multi-component systems can substantially be re-used, if they are recycled into the production process. According to the disclosure in U.S. Pat. No. 4,623,711, liquid polymercaptan polymers of high viscosity can be reacted with organic dimercaptans having a low molecular weight in the presence of organic amines to form liquid polymers which have a low viscosity. Because of their modified terminal groups, these liquid polymers permit the production of cured polymers having a higher stability.
As soon as the individual components of the multi-component systems have contacted each other or the reaction of single-component systems has been started, any resulting solid elastomeric residual or waste materials, which are partly or fully cured, cannot be re-used according to the prior art and were disposed of as waste materials. Such materials have a particularly high stability to light and ozone and to numerous chemicals (See E. Dachselt, Thioplaste, Leipzig, 1971, pp. 50 to 56, and A. Damusis, Sealants, N.Y., 1967, p. 182). In the case of one-component systems such residual materials may form during the production in production plants. During the processing, residual amounts are left in the containers used for the processing, such as cartridges. In the case of one-component or multi- component systems, partly or fully cured residual materials are formed in the material-supplying parts of processing plants, when such plants are being started up or have been shut down or are being cleaned or during the removal of surplus amounts as the material is applied to the structural parts.
Solid elastomers, which cannot be re-used and must be disposed of as waste, also become available at the end of the useful life of structural parts in which these elastomers are used.
Polysulfide or polymercaptan compositions are used, e.g., as sealants or coating compositions. Cured polysulfide and polymercaptan joint-sealing materials must be disposed of as waste materials during a structural alteration, rehabilitation or wrecking of buildings. Polysulfide or polymercaptan sealants used in insulating glass panes must be disposed of as waste materials at the end of the life of an insulating glass pane or when this type of pane has been prematurely removed. Cured polysulfide or polymercaptan sealing materials used in aircraft are disposed of after decommissioning the aircraft. Similarly, polysulfide or polymercaptan coating materials of various kinds become available as waste materials when the corresponding structural parts have been removed. In many cases the disposal is difficult, because the cured elastomers strongly adhere to the substrate.
European Patent Specification 0 188 833 discloses that cured polysulfide sealing materials can be restored to a liquid to pasty state by a depolymerizing composition consisting of an amine and a compound that contains mercapto groups or di- or polysulfide groups. With the help of a solvent for decreasing the viscosity of the composition, that composition can be used to clean processing machines or structural parts by removing residual polysulfide sealing materials. But the resulting decomposition products of the polysulfide sealing materials dissolved in solvents can no longer be cured by the known oxidative curing mechanism for polysulfide or polymercaptan systems and for this reason they cannot be used again for the same or similar purpose and are disposed of as waste material. Because of the solvent content and the components contained in these mixtures of solvents and depolymerized sealing materials, they must be disposed of as hazardous waste materials.